The problems associated with maintaining the cover members of a loose leaf binder spaced apart in parallel relation are well recognized and there have been many prior attempts over many years to provide a satisfactory solution.
For example, U.S. Pat. No. 4,531,764 issued to Chang in 1985 teaches mounting an adjustable closed loop strip inside a cover to provide a spacer. However, the strip must be adjusted with any significant change in the number of papers in the file which procedure can be inconvenient and time consuming. Furthermore, the strip is intended to be permanently adhered to the cover preventing transfer and reuse on other files when the file is completely full and the spacer is not needed. In addition, the strip does not provide a closure member for the file.
In another approach, taught by U.S. Pat. No. 4,744,689, issued to Sternberg in 1988, a spacing block is mounted permanently along a free edge of one cover and hook and eye fasteners releasably secure the other cover to the top of the block. Again transfer from a completely full file to another would not seem to be possible, while a block mounting process would seem to involve an undesirably time consuming manufacturing process and the presence of block may add significantly to the weight of the binder.
Additionally, hook and loop fasteners can, in practice, be relatively difficult and time consuming to open.
In other approaches, taught by U.S. Pat. Nos. 4,569,613 and 4,524,991, issued to Thomas in 1984 and 1983, respectively, a channel section restraining member has clips releasably receiving the entire free edges of the covers along the open side remote from the spine. However, the restraining member must be completely removed from the file each time to open the file to add papers while it can be relatively difficult to align both the entire free edges with the respective clips for forcible receipt therein, particularly if the file is relatively worn and the hinged connection to the spine is weak so that the covers are not precisely aligned with each other or, if the file is slightly overfull, requiring the cover members to be manually forced together.
In an attempt to overcome at least some of the disadvantages of the above-mentioned teachings listed therein, U.S. Pat. No. 4,997,207 issued to Feldman in 1992 specifically directs that any such restraining member be permanently attached to a notebook cover, which is clearly disadvantageous as, when a binder is completely filled, the restraining member may no longer be needed and removal and mounting on the next unfilled or only partially filled binder is desirable.
In addition, the binder relies on a particular construction of detent latching mechanism which requires that the restraining member be depressed into the file along the entire length thereof to fasten and release the latching mechanism which can require difficult manipulation particularly as some papers may be improperly filed obstructing the inner movement of the restraining member or when the-file is slightly overfull. In addition, there would appear to be a risk of the hinge portion weakening in resiliency in use of the binder for an extended period.
In other approaches requiring permanent attachment of spacing members, U.S. Pat. No. 5,002,416 issued to Serzen in 1991, teaches post-form spacing portions which can be broken to required height and are preferably attached by adhesive to upstand from the inside surface of one cover member but do not secure the binder in closed condition; U.S. Pat. No. 501,751 issued to Waring in 1893 teaches loop-form restraining members located to upstand around the entire periphery of the file opening while U.S. Pat. No. 717,842 to Grimes teaches a height adjustable post screw mounted into a cover member requiring an undesirably massive construction, complex and expensive manufacture and relatively time consuming to assemble. The upstanding spacing or restraining members taught by Serzen and Grimes may also impede access to file papers during file use, while the ring catch taught by Grimes may prove relatively difficult to manipulate.
Still other approaches are described in U.S. Pat. No. 5,267,804 filed September 1991 and issued December 1993 to Baumgarten; U.S. Pat. No. 5,069,567 to Fink et al; French 252942 published 1983; German 9002226 published 1983; U.S. Pat. No. 5,067,748 issued 1991 to Wernques; U.S. Pat. No. 4,932,679 issued 1990 to Mayer.
U.S. Pat. No. 2,323,285 issued in 1943 to Trussel teaches the use of keyhole shaped slots in a spine mechanism for releasable retaining resiliently flexible binding rings or loops.